FAQ: How you can still get measles even after being vaccinated

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The Daily Beast recently reported that a woman who was fully vaccinated against measles contracted the disease and exposed 88 other people, four of whom also contracted the highly contagious disease. Two of the sick people were also vaccinated.

In light of California’s current measles outbreak, we talked with two epidemiologists to clear up some questions about the measles and the vaccine.

How effective is the MMR vaccine, which prevents against measles, mumps and rubella?

The vaccine is 95 percent effective, says Dr. George Rutherford, head of the Department of Epidemiology and Biostatistics at of the UCSF School of Medicine.

That means that 5 percent of kids who are vaccinated at age 1 won’t develop immunity. That vaccine failure rate is reduced when kids get a second dose of the vaccine before entering school. Rutherford says it’s also recommended that kids get immunized before college, to further reduce that rate.

What causes the vaccine to fail?

Vaccine failure is rare, but there could have been a problem with the vaccine itself. Maybe medical staff mishandled it, or it was not properly stored – many vaccines have to be refrigerated. Or maybe the correct vaccine was not actually administered, and it was recorded incorrectly in the medical record. It’s also possible that maternal antibodies from breastfeeding blocked the vaccine, Rutherford says.

The Daily Beast reported that a woman who was vaccinated still got measles. She transmitted it to four people, two of whom had also been vaccinated. How could that have happened?

People who are fully vaccinated against measles should consider themselves immune to measles.

But, uncommonly, there are people who never responded to the vaccine, those who needed a second dose to have full immunity, and those whose immunity to measles waned over time, since we’re not naturally exposed to the disease anymore, Rutherford says. If someone comes in very close contact with measles, it’s rare, but possible, for the disease to overcome that person’s level of immunity.

Even in that case, the vaccine should still provide some protection and prevent the serious side effects of measles, that can lead to brain damage and death, says Dr. Susan Huang, medical director for epidemiology and infection prevention at UC Irvine.

I came into contact with someone with measles. What should I do?

If you’re not vaccinated, get vaccinated immediately. If you can’t provide proof of vaccination, or if there’s any question of your vaccination status, you should get vaccinated again, Huang says. She adds that there are exceptions. Generally, adults who born before 1957 grew up at a time when measles was very common and are considered immune.

People who have serious immune issues will need to receive antibody infusions to protect them if directly exposed to measles, Huang says.

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